riff_raff wrote:The performance numbers RR published for the Crecy should be taken with a grain of salt. The Crecy only ran on a test stand, and the total time run by all of the Crecy test engines was less than 200 hours. The Crecy was a high-performance 2T and its high EGTs would have been hard on the turbine materials available at the time. Also, once the Crecy was redesigned for use in an actual aircraft, it would have become much bulkier, heavier, and less efficient than the test rigs.
They should be taken with a grain of salt because they weren't official ratings derived from the 114 hour type test.
The EGT wasn't as high as the combustion temperatures from the WR-1 gas turbine. The Crecy's power recovery turbine was a half scale version of the WR-1.
Weight waise there would be some gains, but largely to do with performance.
Firstly the Crecy had a single speed single stage supercharger.It is likely that a 2 speed version would be required - in the Merlin that change added ~65lb.
The RAE also started doing some performance estimates of aircraft powered by a 2 stage Crecy. That change added a further ~200lb to the weight of the 2 speed Merlin.
Additional weight was gained by the Merlin because of changes to the construction (2 piece block/head -> 1 piece block/head -> 2 piece block/head) and because the engine was originally designed for 87 octane fuel and no more than +6psi boost but by mid war was expected to take +16psi or +18psi boost. In fact, by the end of the war maximum weak mixture cruise was done at +7psi boost.
The Crecy was designed for +18psi boost from the start, so I doubt much weight would be needed for strengthening. The main issues for reliability would have been the overheating pistons (poor cooling oil system - would have been redesigned to have sprays mounted in the block, rather than having the oil exit the top of teh con rod). and the sleeve. Neither of which should add much, if any, weight.
